Above ground biomass yield

Biomass yield is one of the yield components of tef plant and the result of ANOVA indicated that the main effects of N rate and timing of N application highly significantly influenced biomass yield (P≤0.01) as well as the interaction of the two factors (P≤0.05) (Appendix 4). Thus, the increased total biomass yield significantly increased in response to increasing rate of nitrogen and its timing (Table 10). The highest biomass yield (9867.2 kg ha-1) was obtained under in plot supplied with 69 kg N ha-1 in two equal splits (½ dose at sowing and ½ dose at tillering), followed by (7880.6 kg ha-1) was obtained plots treated with 92 kg N ha-1 in two equal split application. Whereas the lowest biomass yield (4960 kg ha-1) was obtained with 23 kg N ha-1 at sowing time, followed by 46 and 92 kg N ha-1 rate in full dose at sowing (Table 10).

Thus, the maximum biomass yield exceeded the minimum biomass yield by about 49.73%. This significantly enhanced biomass yield by nitrogen application is in agreement with the results of Ali et al. (2005) and Iqtidar et al. (2006) who also reported a significant increase in biomass yield of wheat as a result of increased rate of N application. In line with this result, Abraha (2013) reported the highest biomass yield (9004 kg ha-1) under plots supplied with 69 kg N ha-1 applied in two equal splits (½ at sowing and ½ at tillering) whereas, the lowest biomass yield was obtained from plots grown at the lowest rate applied as full dose at sowing.

As compared to 69 kg N ha-1 applied in two split application (½ at sowing and ½ at tillering) the least response in the biomass yield was observed to the highest level of N rate applied in full dose at sowing. The lowest biomass yield might be due to the effect of lodging result from full dose of N fertilizer application that tended to encourage vegetative growth and plant height leading to lodging before the translocation of dry matter to economic yield since biomass includes the economic yield tool. This result is, however, in contrast to that of Haftamu et al. (2009) who found the highest biomass yield of tef in response the application of 92 kg N ha-1. This may be attributed to possible differences in the inherent fertility of the two soils, whereby the soil on which these authors conducted their experiment may have been lower in organic matter than the soil used for this experiment. This may have rendered the later soil to have lower ability to supply N from mineralization, thus requiring the application of more external nitrogen ( 92 kg N ha-1) for increased biomass production of tef than the soil used for this experiment. Generally,

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increasing the rate of nitrogen from 0 to 69 kg N ha-1 significantly increased aboveground biomass by about 68.5%.

Table 10. Mean values of above ground biomass yield of tef (kg ha-1) as affected by rate and timing of nitrogen fertilizer application.

Timing of application (T) N rate kg ha-1 T1 T2 T3 Mean 23 4960.03f 5434.50ef 5869.00def 5421.2c 46 6899.06dbc 7577.80bc 6909.06dbc 7128.6b 69 7459.76bc 7330.60bc 9867.23a 8219.2a 92 6405.63dec 7531.06bc 7880.56b 7272.4b Mean 6431.1b 6968.5b 7631.5a 7010.36c Control 3105.9g R T R*T Treated vs. control LSD ().05) 741.86 642.47 1284.9 1232.7 CV (%) 10.8 10.9

Where, R= rate, T= timing of application, T1= full dose at sowing, T2= full dose at tillering, T3=½ dose at sowing + ½ dose at tillering. Mean sharing the same superscript letter do not differ significantly at P= 0.05 according to the LSD test.

4.5.4 Straw yield

Biological is an important factor because farmers are also interested in straw yield in addition to grain. Straw of tef plant is important in nutrient cycling and livestock feed for the highland farmers. Like biomass yield, straw yield was affected highly significantly by the main effect of N fertilizer rate (P≤0.01) and timing of application (P≤0.01). The two factors interacted significantly (P≤0.05) to influence straw yield (Appendix 4). The maximum straw yield of 7473.3 kg ha-1 was obtained when tef plants were treated with 69 kg N ha-1 in two equal split doses (½ at sowing and ½ at tillering). Whereas, the lowest 3491.5 kg ha-1 was recorded under 23 kg N ha-1 applied in full dose of nitrogen at sowing.

Thus, compared to the straw yield obtained in response to applying 23 kg N ha-1 in same time of application with the tef straw yield obtained in response to applying 69 kg N ha-1 in two equal split doses at sowing and tillering was higher by about 42.2% (Table 11). The increased straw yield might be caused due to the effect of high N application on the production of effective large

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number of tillers, increased plant height and panicle length that might have resulted in increased straw production. However, it was statistically at par with the same straw yield recorded at 92 kg N ha-1 (5986.6 kg ha-1), 46 kg N ha-1 (5880 kg ha-1) and 92 kg N ha-1 (5695.3 kg ha-1), respectively, in two split application (½ at sowing and ½ at tillering) or full application at sowing or at tillering.

Increasing level of N up to 69 kg N ha-1 significantly increased straw yield but decreased at 92 kg N ha-1. This may be attributed the vigorous vegetative growth enhancing property of nitrogen whereby increased number of tiller and dry matter may have been produced due to efficient uptake of the nutrient by the plants over two major growth stages. Similar results were found by Temesgen (2001), Legesse (2004), Mitiku (2008) and Haftamu et al. (2009) who reported that the higher straw yield was obtained in response to the application of higher rates of N application. In agreement with this report, Amsal et al. (2000) reported that N rate significantly enhanced the straw yield of wheat, since N usually promotes the vegetative growth of a plant.

Table 11. Mean values of straw yield of tef (kg ha-1) as affected by rate and timing of nitrogen fertilizer application. Timing of application (T) N rate kg ha-1 T1 T2 T3 Mean 23 3491.46e 3931.00de 4317.16dec 3913.2b 46 5880.76b 5638.70b 4891.73dbc 5470.4a 69 4995.16dbc 5373.43bc 7473.26a 5947.3a 92 4771.63bcd 5695.30b 5986.56b 5484.5a Mean 4784.8b 5159.6ab 5667.2a 5203.8c Control 2242.9f R T R*T Treated vs. control LSD (0.05) 731.37 633.39 1266.8 1217.7 CV (%) 14.37 14.52

Where, R= rate, T= timing of application, T1= full dose at sowing, T2= full dose at tillering, T3=½ dose at sowing + ½ dose at tillering. Mean sharing the same superscript letter do not differ significantly at P= 0.05 according to the LSD test.

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